Joint restraint assembly

ABSTRACT

A joint restraint assembly for connecting pipe ends together, or to other objects, which includes a body encircling the pipe. The body has a plurality of cavities adjacent to the pipe with a segment configured to fit into each cavity. One or more threaded bores are disposed through the body into each cavity. A threaded bolt extends through each threaded bore to engage the segment in that cavity, and to pre-load the segment against the pipe when assembled thereon. Mechanical or pressure loading, tending to pull the pipe out of the restraint assembly, causes the segment to self actuate, and the application of increasing load causes a proportional increase to the force engaging the segment to the pipe. The joint restraint assembly reliably accommodates comparatively high levels of mechanical loading and/or pipe internal pressure, and does so without relying upon the limited force produced by the threaded bolt pre-load on the segments at the time of assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims the benefitunder 35 U.S.C. §121 of, application Ser. No. 10/637,139 filed on Aug.8, 2003 entitled JOINT RESTRAINT ASSEMBLY, and whose entire disclosureis incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a joint restraint assembly. Moreparticularly, the present invention relates to a joint restraintassembly for connecting pipes together, or to other objects.

2. Description of Related Art

Joint restraint assemblies of several types are known in the art andwhich comply with pipe connection standards, such as the ANSI/AWWAC111/A21.11, entitled “American National Standard for Rubber-GasketJoints for Ductile-Iron Pressure Pipe and Fittings.” A conventionalrestraint assembly comprises an annular body having a plurality ofthreaded bolts equally spaced around the body, with the threaded boltsextending through threaded bores disposed through the body along radiallines, or radial lines inclined at an angle of less than 90 degrees fromthe pipe axis. The end of each bolt is configured to directly bear onthe pipe surface or another component that, in turn, bears on the pipesurface. The head of each bolt typically includes a torque head with afeature that is designed to shear when a predefined torque is applied tothe bolt. The shear feature is intended to result in the application ofa specific torque to each bolt without the use of a torque measuringwrench.

Once the joint restraint assembly is positioned adjacent the end of apipe, the pipe end is mated into the socket and then the flange portionof the joint restraint is secured to a corresponding flange portion onthe socket side via flange-connecting fasteners (e.g., “T-bolts”). See,for example, U.S. Pat. Nos. 3,333,872 (Crawford, Sr. et al.); 3,726,549(Bradley, Jr.); 4,848,808 (Pannell et al.) and 4,779,900 (Shumard). Itshould be understood that subsequent reference to “bolt” hereinafterrefers to the bolts used to secure the joint restraint assembly to thepipe end and not to the flange-connecting fasteners used to secure theflanges together unless indicated.

In some conventional restraint assemblies, the end of each bolt iseither configured to penetrate the surface of the pipe or to bear upon apad, clamping block, or segment with one or more gripping teeth topenetrate the surface of the pipe. In conventional restraint assembliesthat utilize segments with one or more gripping teeth to penetrate hardpipe materials, such as ductile iron, the length of the gripping teethpenetrating the pipe surface and the depth of the penetration arelimited by the force produced as a result of applying the specifiedtorque to the threaded bolt. As a result, a conventional restraintassembly applies loading that is localized at the positions of thethreaded bolts or clamping blocks. The allowable mechanical or pressureloading, tending to pull the pipe out of the restraint assembly, islimited by the shear strength of the pipe material and the area of thepipe material that would have to shear in order to permit thepenetrating gripping teeth to slip along the pipe surface, with thatshear area being related to the penetration depth of the gripping teethinto the pipe material and the circumferential length of thepenetration. The allowable mechanical or pressure loading, tending topull the pipe out of the restraint assembly, is also limited by theshear strength of the segment material and the area of the segmentgripping teeth that would have to shear in order to separate thegripping teeth from the segment, with that shear area being related tothe penetration depth of the gripping teeth into the pipe material andthe circumferential length of the penetration. Accordingly, conventionalrestraint assemblies are often inadequate for comparatively high levelsof mechanical loading and/or pipe internal pressure. See, for example,U.S. Pat. Nos. 817,300 (David); 3,333,872 (Crawford, Sr. et al.);3,726,549 (Bradley, Jr.); 4,397,485 (Wood); Des. 294,384 (Endo et al.);

One type of conventional restraint assembly in the prior art comprisesan annular body having a plurality of cavities adjacent to the pipe witha clamping block configured to fit into each cavity. See, for example,U.S. Pat. Nos. 4,092,036 (Sato et al.); 4,779,900 (Shumard); 4,896,903(Shumard) and 5,071,175 (Kennedy, Jr.). A plurality of bolts equallyspaced around the body, disposed through the body along radial linesinclined at an angle of less than 90 degrees from the pipe axis, thatextend through non-threaded oval holes into the cavities. The inboardsurface of each cavity is perpendicular to the axis of the oval holesuch that it is inclined to the axis of the pipe. Each bolt isconfigured with an integral annular flange, or collar, that is slidablyin contact with the inclined surface of the cavity, and the threadedshank of each bolt is engaged in a threaded hole in the correspondingclamping block. Each clamping block is configured with teeth to directlybear on the pipe surface. When the threaded bolt is turned, force isapplied to the clamping block causing the teeth to dent the pipesurface. An equal and opposite force is applied to the contact betweenthe integral annular flange of the bolt and the inclined surface of thecavity. These contact surfaces are not polished and lubricated, and theyare usually covered with a protective coating. (See for example EBAAIron Sales, Inc., Wedge Action Megalug™ Field Installed Joint Restraint;EBAA Iron Sales, Inc., Series 3000 Multi-Purpose Wedge Action Restraint;or EBAA Iron Sales, Inc., Series 2000PV Megalug™ Retainer Glands for PVCPipe with Cast-Iron or I.P.S. Outside Diameters with M. J. Bells). Theservice environment ordinarily results in corrosion, sedimentparticulate and other conditions that do not permit a low coefficient ofsliding friction between the integral annular flange of the bolt and theinclined surface of the cavity.

The concept of this “wedge” type of restraint assembly is that as themechanical or pressure loading tends to pull the pipe out of therestraint assembly, the annular flange on the threaded bolt slides alongthe inclined surface of the cavity causing the clamping block teeth todent the pipe surface more deeply, thereby resisting the tendency of thepipe to pull out of the restraint assembly. In practice, the frictionalforces that resist sliding between the annular flange on the bolt andthe inclined surface of the cavity are proportional to the force beingapplied to dent the pipe and, in combination with the mis-alignment ofthe force vectors tending to cause the annular flange of the bolt tobind instead of slide, the theoretical effect is only partiallyrealized. All of the “wedge” type prior art has this inherentcharacteristic which limits its effectiveness. One manufacturer of thistype of joint restraint assembly explains in its publications that thistype of restraint works without wedge movement to resist normaloperating pressure in the pipe, but wedge movement responds “only as theexternal force is increased” from additional external conditions such assubsidence, waterhammer, traffic loads or small tremors (EBAA IronSales, Inc., Wedge Action Megalug™ Field Installed Joint Restraint).However, in the normal operation of this type of restraint assembly, theforce generated by the bolt is applied to the clamping block causing itsteeth to dent the pipe surface, and if the wedge effect is able toovercome its inherent sliding friction and binding characteristics, itdoes so, inefficiently, only under additional external loadingconditions.

Another type of conventional restraint assembly in the prior artcomprises an annular body with equally spaced cavities with a segmentconfigured to fit into each cavity. A threaded bolt extends through athreaded bore into each cavity, and the force generated by the threadedbolt is applied to the segment to cause the edges of the segment to dentthe pipe surface. The end of the threaded bolt is manufactured with ahemispherical form, and it fits into a dished socket in the segment.(See Sigma/Napco, SuperLug™, Pipe Restraints for Ductile Iron Pipe). Themanufacturer's publications state that: the ball and socket allows lugdeflection at any angle, thereby allowing the lugs to “rock”, actuallygripping the pipe more securely as pressure-induced load increases; andpressure-induced load causes the primary contact edge of the SuperLug™teeth to “grab” the pipe surface, further increasing pressure-inducedload restraint.

However, testing of this design in larger sizes, such as for 30 to 48inch diameter pipes, revealed that the force of the radial threadedbolt, even in combination with the “rocking” or “cam action”, wasinsufficient to adequately grip the pipe, and other undesirable effectsoccurred such as bending of the threaded bolt. A parametric analysis ofthe design revealed that the pressure-induced load, tending to pull thepipe out of the restraint assembly, overpowered the capability of thedesign as the pressure-induced load increased with the square of thepipe diameter. Using a restraint assembly for 48 inch pipe as anexample, the total axial load is in excess of 1,000,000 pounds duringthe hydrostatic proof test at 500 psi pressure. This requires each of 32segments, and the threaded bolt forcing it into the surface of the pipe,to resist almost 32,000 pounds of pressure-induced load. When tightenedto the specified torque, the threaded bolt is capable of applying 7,500pounds of force to the segment, causing its edges to dent the surface ofthe pipe, but the indentation was not of sufficient depth andcircumferential length to resist the 32,000 pounds of pressure-inducedload. With the known shear strength of the pipe material, the requiredshear area of the pipe material that would have to resist shearing inorder to prevent the penetrating, gripping teeth from slipping along thepipe surface, requires both a greater depth of penetration into the pipematerial and a greater circumferential length of that penetration.

It would be desirable for a restraint assembly to overcome the inherentproblems and limitations in the prior art and reliably accommodatecomparatively high levels of mechanical loading and/or pipe pressure,and to do so without relying upon the limited force produced by theapplication of the specified torque to the threaded bolts.

The entire disclosures of all of the references cited herein areincorporated by reference.

BRIEF SUMMARY OF THE INVENTION

A joint restraint assembly for connecting pipe ends together, or toother objects, by gripping the outer surface of the pipe. The jointrestraint assembly comprises: a body encircling the pipe, with the bodyhaving a plurality of cavities adjacent the pipe and at least one set ofa corresponding plurality of threaded bores disposed through the body,and wherein each threaded bore of the at least one set of acorresponding plurality of threaded bores is in communication with arespective cavity; a segment disposed within each of the cavities in thebody, and configured to make contact between the body and the surface ofthe pipe so as to provide resistance to pipe pull-out in proportion tothe mechanical and/or internal pressure loading applied to the pipe(e.g., a self-actuating member); and a threaded bolt extending througheach of the threaded bores to pre-load the respective segment intoinitial contact with the pipe surface.

A method for providing a joint restraint assembly with resistance topipe pull-out in proportion to the mechanical and/or internal pressureloading applied to a pipe. The method comprises the steps of: providinga body that encircles the pipe wherein the body has a plurality ofcavities and at least one set of a corresponding plurality of threadedbores disposed through the body, with the cavities being disposedadjacent the pipe; disposing a segment within each of the cavities;pre-loading the segment against the pipe by rotating a correspondingbolt disposed in each threaded bore of the at least one set of acorresponding plurality of threaded bores; permitting the segment tomove within the cavity, independently of the bolts, in response to pipepull-out forces, and wherein the segment is self-actuating and orientsitself so that the segment is in contact with the body and the pipesurface and generates a resistance to the pipe pull-out forces inproportion to the mechanical and/or internal pressure loading applied tothe pipe.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the followingdrawings in which like reference numerals designate like elements andwherein:

FIG. 1 is an elevation view, or end view opposite the gasket side, of ajoint restraint assembly embodying the present invention;

FIG. 1 a is an elevation view, similar to the view of FIG. 1, showingonly the joint restraint assembly body;

FIG. 2 is an elevation section view of the joint restraint assembly bodytaken along section plane A-A of FIG. 1 a;

FIG. 3 is a section view taken through the center of a threaded bore andsegment, along section plane C-C of FIG. 1, showing the segment inposition for shipping and assembly onto a pipe;

FIG. 4 is a section view taken through the center of a threaded bore andsegment, along section plane C-C of FIG. 1, showing the segment duringpre-loading on the surface of a pipe;

FIG. 5 is a section view taken through the center of a threaded bore andsegment, along a section plane, similar to section plane C-C of FIG. 1,showing the segment in contact with the surface of a pipe and aninterior corner of the cavity, the force vectors on the segment intransmitting the mechanical and/or pipe internal pressure loading whilein use, and the self-actuating effect of the configuration;

FIG. 6 is a section view taken through the connecting aperture in theflange portion of the body, along section plane B-B of FIG. 1, showingthe basic tee shape of the pipe restraint body;

FIG. 7 is a section view of a second embodiment of the segment of thepresent invention taken along a view line similar to section plane C-Cof FIG. 1, showing the self-actuating operation; and

FIG. 7 a is a section view of a third embodiment of the segment of thepresent invention taken along a view line similar to section plane C-Cof FIG. 1, showing the self-actuating operation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a joint restraint assembly. Moreparticularly, the present invention relates to a joint restraintassembly for connecting pipes together, or to other objects. Althoughthe following description of the preferred embodiment is considered bythe inventors to be the best mode of carrying out the invention, theclaims presented below are not limited to the particular details of thedescribed embodiment. Many variations of the particular details of thedescribed embodiment may be apparent to those skilled in the art whichwould provide for construction of the joint restraint assemblyincorporating the principles of the present invention as claimed.

The present invention provides a joint restraint assembly suitable forconnecting pipe that is subjected to comparatively high levels ofmechanical loading and/or pipe internal pressure. The assembly includesa body encircling the pipe, with said body having a plurality ofcavities adjacent to the pipe. A segment is configured to fit into saidcavity and one or more threaded bores are disposed through the body intoeach cavity. A threaded bolt extends through said threaded bore toengage the segment in that cavity. The threaded bolt has a head suitablefor applying torque to the bolt and may include a feature to limit themaximum torque which can be applied. When the specified torque isapplied to the bolt head at the time of assembly, the force developed bythe bolt serves to pre-load the segment against the pipe. Mechanicaland/or pressure loading, tending to pull the pipe out of the restraintassembly, causes relative movement between the pipe and the restraintassembly. This relative movement causes the segment to firmly contactthe interior corner of the cavity, and the application of increasingload and the associated relative movement, causes the segment to rotateresulting in a proportional increase to the force engaging the segmentto the pipe. This action of the segment is herein referred to asself-actuating. It should also be understood that subsequent referenceto “mechanical and/or pressure loading” hereinafter includes therelative movement between the pipe and the joint restraint assembly thatoccurs as a result of the application of the mechanical and/or pressureloading. It should be further understood that this relative movement isnot to be confused with slippage of the restraint assembly along thesurface of the pipe.

The segment is configured to contact the surface of the pipe. Thesegment may function in a manner similar to a cam, pawl, dog, or otherself-actuating member, and it may possess a surface treatment (e.g., aknurled surface) intended to reduce the likelihood of slipping on thepipe surface. To minimize the likelihood of slipping on the pipesurface, the segment of the preferred embodiment is configured with oneor more edges capable of penetrating the external surface of the pipeEach edge is circumferentially-contoured to approximately match thecurvature of the pipe. The segment, and each edge thereon, is ofsufficient circumferential length to distribute the applied loading overa substantial portion of the pipe periphery. The segment possesses aform wherein the application of mechanical loading or pipe internalpressure causes the corner of the segment to contact an interior cornerof the cavity to serve as a pivot for the segment. As a result, theloading transmitted from the pipe through the edge of the segment istransmitted to the corner of the segment in contact with the interiorcorner of the cavity. Accordingly, the loading from the edge of thesegment, through the segment, to the corner contact location produces astate of stress in the segment that is primarily compressive.Transmitting the loading in this manner minimizes the tendency of thesegment material to fracture. The relief angle adjacent to each edge ofthe segment, as measured from the pipe surface, is optimized to maximizethe load transmission capability from the segment edge into the segmentbody while permitting the segment edge to penetrate the pipe surfacesufficiently to prevent slippage of the joint restraint assemblyrelative to the pipe.

With this segment configuration, the function of the threaded bolt isreduced to pre-loading the segment against the pipe surface, at the timeof assembly, sufficiently to resist handling loads and low levels ofinternal pipe pressure. Upon the application of sufficient mechanicaland/or internal pressure loading, a corner of the segment is caused tofirmly contact an interior corner of the cavity, and the continuedapplication of mechanical and/or internal pressure loading causesadditional rotation of the segment between the interior corner of thecavity and the pipe surface. In doing so, the segment performs in aself-actuating manner where the force tending to cause the segment edgeto penetrate deeper into the pipe surface is proportional to theincrease in mechanical and/or internal pressure loading. Accordingly,the entire length of the segment edge is caused to penetrate deeper intothe pipe surface as required to resist the applied loading, well beyondthe penetration achievable from the force applied by the threaded boltalone or any prior art arrangement. The threaded bolt does notcontribute to securing the joint restraint assembly onto the pipe duringhigher levels of loading.

The self-actuating function of the segment produces internal forcevectors with, in part, force vector components parallel to the surfaceof the pipe that resist movement due to the mechanical and/or internalpressure loading on the pipe tending to pull the pipe out of the jointrestraint assembly. The body of the joint restraint assembly includes aradial flange having multiple axial apertures, equally spaced around thebody, through which the flange-connecting fasteners are installed tosecure the joint restraint assembly to another restraint assembly oranother object. The difference in the radial positions of the forcevector component parallel to the surface of the pipe, applied to theinterior corner of the cavity, and the axial restraint force of theflange-connecting fasteners is small in comparison to conventional jointrestraint assemblies.

The force vectors internal to the segment, produced by itsself-actuating function, also have force vector components that areperpendicular to the pipe surface, and it is this vector componentapplied at the edge of the segment that forces the segment edge topenetrate the surface of the pipe. The corresponding force vectorcomponent perpendicular to the pipe surface, applied to the interiorcorner of the cavity, substantially adds to the loading applied radiallyto the joint restraint body. Accordingly, the configuration of the bodyis optimized to resist this additional loading and the tendency of thebody to roll about an axis through its cross-sectional center of area.The optimum body cross-section is in the shape of a tee, with the top ofthe tee being adjacent to the surface of the pipe and the leg of the teeforming the radial bolt flange of the joint restraint assembly. Thisbasic shape was modified as required to incorporate the cavities,threaded bores and seal features into the body.

Elastomeric material is installed between each end of the segment andthe corresponding walls of the cavity in order to retain the segment inposition for shipping, handling and installation. Elastomeric materialis also installed between one face of the segment and its correspondingwall of the cavity in order to pre-position the segment against theopposite wall of the cavity. Accordingly, the segment is pre-positionedfor appropriately making contact with the interior corner of the cavityand the pipe surface, as pre-loaded by the threaded bolt, so as toestablish the self-actuating position of the segment.

The joint restraint assembly of the present invention can be configuredto fit pipes of any size or material, and to join or attach to any othertype of restraint, sealing assembly or other object. The joint restraintassembly can be made from any suitable material or combination ofsuitable materials. For example, the present invention can be made fromductile iron.

In particular, an elevation view, or end view opposite the gasket side,of a joint restraint assembly 1 embodying the present invention is shownin FIG. 1. Joint restraint assembly 1 comprises a substantially circularbody 2, or gland, that is slipped over the end of a pipe (not shown),and a gasket (not shown) is then slipped over the end of the pipe. Thebody 2 (shown in FIG. 1 a) comprises connecting apertures 3 disposedthrough body 2 generally parallel to the longitudinal axis of the pipe.Flange-connecting fasteners (not shown), typically T-bolts, extendthrough the connecting apertures 3 to connect the joint restraintassembly 1 to another pipe or fitting (not shown).

As shown in FIG. 2, the body 2 of the joint restraint assembly 1 alsocomprises a plurality of cavities 4 adjacent to the surface of the pipe(not shown). A threaded bore 5 extends radially through body 2 into eachcavity 4. A segment 6 is positioned within each cavity 4 in body 2 asshown in FIG. 3. A threaded bolt 7 extends through threaded bore 5 inbody 2 to contact segment 6. The threaded bolt 7 comprises a reducedsection 8 between an outboard hex head 9 and an inboard hex head 10,such that as torque is applied to outboard hex head 9, reduced section 8shears at a pre-determined torque, and inboard hex head 10 remainsattached to threaded bolt 7 for subsequent withdrawal of same, ifneeded. The end 11 of threaded bolt 7 is rounded to localize the contactwith segment 6.

As shown in FIG. 3, assembled for shipping/handling and installation andslipping over the end of a pipe, each segment 6 is containedsubstantially within cavity 4 in body 2, with one corner 12 of segment 6positioned in a corresponding interior corner 13 of cavity 4.Elastomeric material 29 is positioned between the sides of segment 6 andthe walls of cavity 4 to maintain the segment in an optimum position forself-actuation.

After joint restraint assembly 1 and a gasket (not shown) are properlypositioned on the end of a pipe 14, all the threaded bolts 7 aresequentially and uniformly tightened to pre-load segments 6 against thepipe surface 15 as shown in FIG. 4. As each segment 6 is pre-loadedagainst pipe surface 15, the edge 16 of segment 6 makes a smallindentation into the pipe surface 15. Pre-loading each segment 6 againstthe pipe surface 15 is complete when reduced section of the respectivethreaded bolt 7 shears from the application of pre-determined torque tohex head 9.

The application of mechanical load to the pipe and/or pressure withinthe pipe produces pipe pull-out load 17 as indicated in FIG. 5, withresulting relative movement between the pipe and the restraint assembly,as described previously. The resisting load 18 is provided by theflange-connecting fasteners (not shown) extending through connectingapertures 3 in body 2. These opposing loads 17 & 18 cause corner 12 ofsegment 6 to load against interior corner 13 of cavity 4 to serve as apivot, and edge 16 of segment 6 penetrates deeper into the pipe surface15.

Pipe pull-out load 17 is applied longitudinally to segment 6 throughforce vector component 20. The direction of force vector 19 is definedby the geometry between the penetrating segment edge 16 and pivot corner12, and the magnitude of force vector 19 is dependent upon this angleand the magnitude of vector component 20. The radial component 21 offorce vector 19 is similarly dependent on the geometric angle of forcevector 19 and its magnitude. Accordingly, radial vector component 21 isalso dependent on the magnitude of vector component 20 and, in turn,pull-out load 17. The radial vector component 21 causes the segment edge16 to penetrate pipe surface 15. As a result, after overcoming thecomparatively small pre-load provided by threaded bolt 7, the depth ofpenetration of segment edge 16 into pipe surface 15, and thus theability to resist pipe pull-out load 17, is directly proportional to themechanical and/or internal pressure loading applied to the pipe—i.e.,the mechanism is “self-actuating.” Under these conditions, the threadedbolt 7 no longer contributes to the ability of the joint restraintassembly to resist the pull-out load 17, and threaded bolt 7 is notsubjected to pull-out load 17 or damage therefrom; note in FIG. 5 thatthe rounded end of the threaded bolt 7 is no longer in contact with thesegment 6. Thus, the self-actuating feature of the segment 6 operatesindependently of the threaded bolt 7.

Force vector 19 is transmitted through segment edge 16 to segment pivot12 as force vector 22, thereby loading the segment edge primarily incompression. Force vector 22 has a longitudinal vector component 23,equal to both the pull-out load 17 and vector component 20, thattransmits the load from segment 6 to body 2 at the cavity interiorcorner 13. Force vector component 23 is resisted by longitudinal forcevector 18 from the flange-connecting fasteners (not shown) extendingthrough connecting apertures 3 in body 2.

Force vector 22 has a radial vector component 24 that is equal to radialvector component 21. Vector component 24 is resisted by circumferential(hoop) stress induced within circular body 2. The distance betweenvector component 24 and the centroid 25 of the cross-section of body 2tends to cause rolling of body 2 about its own centroidal axis. Thedistance between vector component 23 and resisting force vector 18 alsotends to cause body 2 to roll in the same way. Accordingly, body 2 isshaped as shown in FIG. 6 to resist these circumferential and “rolling”stresses. The shape for body 2 found to be near optimum in resistingvector components 23 and 24 comprises a cylindrical portion 26 adjacentto the pipe surface 15 and a radial flange 27, perpendicular to thecylindrical portion, to serve as the flange for the flange-connectingfasteners (not shown). Thus, the basic cross-section of body 2 found tobe near optimum was that of a Tee, with connecting apertures 3 disposedthrough the radial flange portion of body 2. Of course, this basic shapewas altered in the vicinity of each cavity 4 as necessary to accommodatea segment 6 and threaded bore 5 as shown in FIG. 2 and FIG. 3.

The ability of segment edge 16 to penetrate pipe surface 15 is dependenton relief angle 28 as illustrated in FIG. 3. The maximum relief angle 28is determined by the shape of segment 6 that produces a load paththrough segment edge 16 that is primarily compressive, to avoid loadingthe edge in shear. The optimum relief angle 28 is in the range of 25° to35°.

It should be understood that the circumferential length of the pluralityof segments 6 and their edges 16 comprises a substantial portion of thepipe periphery, thereby distributing the force transmitted throughcontact with the pipe more uniformly around the pipe periphery, anddistributing the force transmitted through contact with the body moreuniformly around the body.

FIGS. 7 and 7 a show other segment configurations that provide this“self-actuating” feature which provides resistance to pipe pull-out inproportion to the mechanical and/or internal pressure loading applied tothe pipe. In particular, the segment 6A comprises a cam-shaped memberwhich is initially pre-loaded via the threaded bolt 7, as discussedpreviously with regard to segment 6. As the mechanical and/or internalpressure loading increases, and relative movement occurs between thepipe and the restraint assembly, a cam surface 16A rotates against thepipe surface 15 and transfers the load, causing the corner 12 of segment6A to load against interior corner 13 of the cavity 4. Again, thisaction occurs independently of the threaded bolt 7. Similarly, thesegment 6B comprises a cam-shaped member having a surface texture 16B(e.g., knurled surface) that engages the pipe surface 15. As themechanical and/or internal pressure loading increases, the textured camsurface 16B of the segment 6B rotates against, and penetrates, the pipesurface 15, and transfers the load, causing the corner 12 of segment 6Bto load against interior corner 13 of the cavity 4. Again, this actionoccurs independently of the threaded bolt 7. Thus, it should beunderstood that the self-actuating segment of the present invention canbe achieved using different segment configurations that are (1)pre-loaded by the threaded bolt 7 and (2) that engage the pipe surface15 and body 2 to provide resistance to pipe pull-out in proportion tothe mechanical and/or internal pressure loading applied to the pipe,independent of the threaded bolt.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A method for providing a joint restraint assembly with resistance topipe pull-out in proportion to the mechanical and/or internal pressureloading applied to a pipe, said method comprising the steps of:providing a body that encircles the pipe wherein the body has aplurality of cavities and at least one set of a corresponding pluralityof threaded bores disposed through said body, said cavities beingdisposed adjacent the pipe; disposing a threaded bolt through each ofsaid threaded bores; disposing a segment within each of said cavities;pre-loading a first portion of each segment against an outer surface ofthe pipe by rotating said corresponding bolt disposed in each threadedbore; and generating a resistance to pipe pull-out forces in proportionto the increased mechanical or internal pressure loading applied to thepipe by pivotal motion of each of said segments, said pivotal motionoccurring while losing contact with said threaded bolts.
 2. The methodof claim 1 wherein said step of generating a resistance to pipe pull-outforces comprises permitting said segment to pivot about a second portionthat maintains contact with a corner of said cavity, while losingcontact with its corresponding bolt, as mechanical or internal pressureloading applied to the pipe increases pipe pull-out forces, said firstportion of said segment being driven deeper into the outer surface ofthe pipe in proportion to the applied mechanical or internal pressureloading, said segment resisting pipe pull-out in proportion to theincreased mechanical or internal pressure loading applied to the pipe.3. The method of claim 2 wherein said step of permitting said segment topivot about a second portion comprises loading said segment primarily incompression between said body and the outer surface of the pipe.
 4. Themethod of claim 1 further comprising the step of optimizing said body toresist forces imparted to by contact with said segments.
 5. The methodof claim 4 wherein said step of optimizing said body comprises:providing a substantially cylindrical portion of said body adjacent thepipe surface with a flange extending radially therefrom; and providing abody shape and wall thickness that compensates for the presence of saidcavities for maintaining strength and rigidity of said body.
 6. Themethod of claim 1 wherein said step of pre-loading a first portion ofeach segment against an outer surface of the pipe comprises engaging asegment edge against said outer surface wherein said segment edge formsa relief angle, as measured from the outer surface of the pipe, in therange of 25 to 35 degrees.
 7. The method of claim 1 wherein a secondportion of said segment contacts a corner of said cavity and whereinsaid first portion comprises a cam surface that contacts an outersurface of the pipe and wherein said step of generating a resistance topipe pull-out forces comprises permitting said segment to pivot aboutsaid second portion that maintains contact with the corner of saidcavity, while losing contact with its corresponding bolt, as mechanicalor internal pressure loading applied to the pipe increases pipe pull-outforces, said cam surface rotating against, but not substantiallypenetrating, the outer surface of the pipe in proportion to the appliedmechanical or internal pressure loading, said segment resisting pipepull-out in proportion to the increased mechanical or internal pressureloading applied to the pipe.
 8. The method of claim 7 wherein said stepof permitting said segment to pivot about a second portion comprisesloading said segment primarily in compression between said body and theouter surface of the pipe.